The present invention relates to an ink jet recording apparatus which operates to print an image by applying ink drops discharged from an electrode of a recording head to a recording medium.
An apparatus which discharges liquid ink as small droplets and deposits them on a recording medium so as to record an image by forming dots in a designated pattern has been put to practical use as an ink jet printer. This ink jet printer has the capability of make little noise compared with other recording methods and to record an image directly on a recording medium. Therefore, there is an advantage that this printer can be constructed of a smaller number of parts than that of other recording methods.
A method which has recently received attention, in which the ink is discharged by using the electrostatic force, is disclosed in the PCT National Publication No. 7-502218 (1995). More specifically, a method of producing an ink discharge after the concentration of the coloring material particles is improved by using ink which contains electrified coloring material particles is disclosed in this official report.
In the recording head used in this method, a plurality of ink-discharge electrodes are arranged on one insulated substrate at regular intervals, and an individual pulse drive circuit is connected to each ink-discharge electrode. The pulse drive circuit is controlled so as to superimpose a pulse voltage Vp or the voltage applied to the ink-discharge electrode independently according to the print data supplied from a personal computer etc. The advantage of this method is that the amount of ink being discharged can be controlled by changing the width of the pulse voltage, and the gradation of the color image can be expressed by controlling the area of the record dot formed on a recording medium. Japanese Patent Application Laid-Open No. 10-296979 discloses an example of such a recording head, in which the discharge electrode and the electric field concentration auxiliary electrode are alternately arranged on the recording head.
In the method disclosed in the PCT National Publication No. 7-502218 and the Japanese Patent Application Laid-Open No. 10-296979, a voltage of about 1.5-2.0 kV is applied to all the ink-discharge electrodes as an electrode bias, and a pulse voltage of about 600V is superimposed on this bias voltage applied to the ink-discharge electrode when ink is discharged. Further, because ink is discharged from a plurality of ink-discharge electrodes at the same time, it is essential to provide a driving circuit for switching and controlling the pulse-like high voltage applied to these ink-discharge electrodes. However, an element, such as a field-effect transistor (FET) of the high voltage type is necessary for switching a pulse voltage of about 600V, as mentioned above.
As for the driving circuit which uses such an element, the scale increases.
Although a general-purpose high voltage IC may be used in place of a FET to reduce the circuit scale and achieve a low-priced device, the switching voltage limit is 300V or less in such a high voltage IC. Therefore, it is necessary to discharge ink at the pulse voltage of 300V or less if the driving circuit is provided with a general-purpose high voltage IC in the ink jet recording apparatus of this method. In a technique disclosed in Japanese Patent Application Laid-Open No. 10-138491, a gate electrode having a plurality of gate halls arranged monotonously in a row is provided in front of the record electrode as a means for solving such a problem.
Because a pulse with a reversed polarity is applied to a corresponding gate electrode according to the method of the above-mentioned Japanese Patent Application Laid-Open No. 10-138491 when a voltage is applied to the record electrode, it is possible to reduce the drive voltage to one-half. However, when the record electrode and the gate hall on the gate electrode are arranged with the same spacing, a position adjustment of high accuracy is needed. Therefore, the production cost of the recording head increases, because the manufacturing technology having a high processing accuracy is needed.
Further, there is a problem in that the ink tends to produce a bridge (liquid junction) between the point of the record electrode and the gate electrode, so that ink discharge becomes impossible, due to the fact that the state of flight of the ink droplets becomes unstable because of turbulence when the ink is discharged from the point of the record electrode.
In consideration of the above-mentioned problems, the present invention adopts the following configuration. An ink jet recording apparatus comprises a plurality of ink-discharge electrodes; a control electrode arranged between adjoining ink-discharge electrodes; an opposed electrode arranged at an opposed position with a fixed spacing from the points of said plurality of the ink-discharge electrodes; a power supply connected to said plurality of ink-discharge electrodes and said control electrodes; a first pulse drive circuit connected to said plurality of ink-discharge electrodes; and a second pulse drive circuit connected to said control electrodes; wherein said the second pulse drive circuit outputs a pulse voltage with a reversed polarity to that of said first pulse drive circuit.
Further, the present invention adopts the following configuration. An ink jet recording apparatus comprises a plurality of ink-discharge electrodes; a control electrode arranged between adjoining ink-discharge electrodes; an opposed electrode arranged at an opposed position with a fixed spacing from the points of said plurality of ink-discharge electrodes; a migration electrode arranged on the opposite side of said opposed electrode with respect to said ink-discharge electrodes and said control electrodes; a first power supply connected to said plurality of ink-discharge electrodes and control electrodes; a second power supply connected to said migration electrode; a first pulse drive circuit connected to said plurality of ink-discharge electrodes; and a second pulse drive circuit connected to said control electrodes; wherein said second pulse drive circuit outputs a pulse voltage with a reversed polarity to that of said first pulse drive circuit.
By adopting the above-mentioned configuration, the present invention can provide an ink jet recording apparatus in which the voltage drive method for decreasing the ink-discharge pulse voltage to a voltage level at which the switching can be performed using a general-purpose high voltage IC.